1. Field
The present invention relates generally to communications, and more specifically, to communication devices with switched antenna transmit diversity.
2. Background
In wireless communications, transmitted signals are reflected and scattered by obstacles in their path, often resulting in multiple copies of the signal arriving at the receiver at different times. Depending on the location of the receiving antenna relative to the transmitting antenna, and the obstacles in the signal path, the multiple copies of the signal may combine constructively or destructively at the receiving antenna. In narrow band mobile applications, this phenomenon may cause fluctuations in the signal when the user travels even a small distance. This is often referred to as fast fading. The use of a wide band code division multiple access (CDMA) signal may significantly reduce the impact of fast fading. CDMA is a modulation and multiple access scheme based on spread-spectrum communications which is well known in the art.
Another technique to mitigate fast fading in mobile applications is to use multiple antennas to increase the gain of the signal due to spatial diversity of the antennas. Currently, there are a number of commercially available mobile devices with dual antenna arrangements. However, these mobile devices employ spatial diversity combining techniques for the received signal only, using a single antenna to transmit. In these mobile devices, it would be advantageous to employ a methodology that uses both antennas to achieve transmit antenna diversity.